A vehicle is able to be equipped with a belt-warning system, also known as a seatbelt reminder. For example, seat mats for measuring the seat occupancy can be used in this context because only an occupied seat is usually relevant for a belt warning. The seat mats, for instance, can distinguish between different groups of persons, such as between a baby in an infant seat, a child, or an adult. In addition to seat mats, belt-buckle sensors for detecting an unlocked or locked state of a belt buckle are known as well, as are camera systems for monitoring the passenger compartment of a vehicle.